This invention relates to a platen fixing apparatus for fixing a platen to the frame of a printer.
Generally, a printer has a platen which is rotatably coupled to the frame of a printer. The platen comprises a cylindrical body made of elastic material such as rubber, and a platen shaft inserted in the cylindrical body, with its ends projecting from both ends of the cylindrical body. Each end of the platen shaft is inserted rotatably in a bushing. This bushing is held unrotatably in a supporting hole made in the frame. A snap ring mounted at each end of the platen shaft to restrain the bushing from moving in the axial direction of the platen shaft.
With the above construction, the snap rings need to be attached to the platen shaft in order to mount the platen to the frame, and also must be detached from the platen shaft in order to remove the platen from the frame. It is rather cumbersome to attach and detach the rings to and from the shaft. Further, either snap ring cannot prevent a radial play of the bushing in the supporting hole, and the platen can hardly be attached to the frame in a sufficient stability.
With other conventional platen fixing apparatuses, each end of the platen shaft is inserted rotatably into a bushing, which is mounted in a support recess formed in the frame. A retaining arm is mounted rotatably at one end on the frame and connected thereto by means of a screw. After the bushing is fitted in the supporting recess, the retaining arm is turned to a position where its other end is pressed on the circumferential surface of the bushing. Under this condition, the bushing is held fixedly by the retaining arm in the supporting recess, provided the retaining arm is firmly connected to the frame by means of the above-described screw.
With a platen fixing apparatus of the above construction, it would be troublesome to mount a platen on a frame or dismount it therefrom since the screw of the retaining arm must be tightened or loosened. In addition, the retaining arm is fixed to the frame by one-point support with a screw, and there is a possibility that the retaining arm may turn in the direction of separating from the bushing, making it difficult for the platen to be fixed stably.